Gas metal arc welding, commonly referred to as "GMAW" or "MIG" welding, is an electric arc welding process in which the arc is shielded from the ambient atmosphere by a gas or a mixture of gases. Metal is transferred to a workpiece through the arc from a consumable wire electrode. The consumable wire electrode is continuously fed into the arc at a preselected speed corresponding to a given deposition rate for a given wire size.
There are several different modes of metal transfer which are used with gas metal arc welding. The short circuit transfer mode is a gas metal arc welding process wherein the consumable wire electrode is deposited during repeated short circuits. In the globular transfer mode, molten metal is transferred in large drops from the consumable electrode across the arc. The spray transfer mode involves metal transfer in which molten metal from the consumable electrode is propelled axially across the arc in small drops. The pulsed spray transfer mode is an arc welding process variation wherein the current is pulsed to utilize the advantages of the spray mode of metal transfer at average currents equal to or less than the globular to spray transition current.
Gas metal arc welding is becoming a preferred type of welding because the continuously fed electrode enables the attainment of a greater metal transfer rate over that attainable with totally manual welding methods as well as attaining a greater operator duty cycle.
In some welding applications the appearance of the weld is of prime importance. Such applications include the welding of articles made of stainless steel which generally require a polished appearance. In addition, for a welded article which undergoes sterilizing or cleaning, a smooth weld surface is required to facilitate such sterilizing or cleaning. Heretofore it has generally been necessary to employ gas tungsten arc welding in order to achieve the requisite appearance for welds on metal used for applications which require a very smooth surface. This method is costlier than gas metal arc welding due to the increased labor cost and the slower metal deposition rate inherent in this method.
Accordingly it is an object of this invention to provide a gas metal arc welding method which produces a weld having an appearance comparable to that attainable with gas tungsten arc welding at a higher weld deposition rate.
It is another object of this invention to provide a shielding gas mixture for gas metal arc welding which enables the attainment of welds having an improved appearance over welds attainable with known shielding gas mixtures.